text:
How can I ensure that I have a mode C transponder?
How can I make sure my aircraft is equipped with a mode C transponder?
======================
If a transponder has an ALT button does that mean that the aircraft is equipped with MODE C?

As long as its paired with the appropriate altitude encoder to feed pressure altitude data to the transponder, then yes.

For any aircraft you should check the accompanying POH for a full equipment list of what the plane has been outfitted with. Likewise you should be alert for any place cards noting defective or inoperative equipment. You should also check the aircrafts logs to make sure the transponder has been properly inspected according to § 91.413 ATC transponder tests and inspections and that it is operable. Just because you have one does not mean its legal to fly with. A transponder capable of Mode-C (altitude encoding) needs to either be connected to an altitude encoding altimeter or a blind encoder to report altitude. You should be able to find this out in the POH, if its not connected to one of these two units it will behave like a Mode-A transponder. You can find a  discussion on the various setups here. If you are really curious about how Mode-A/Mode-C communication works this is a pretty good read.
Specific to the Garmin unit you have pictured you can get it to display the aircrafts altitude by pressing the "func" button (pressure altitude that is) and compare with your altimeter. If the unit has a readout it then an pressure unit can be assumed to be connected. NOTE: This is not an official test by any means.

I believe you mean "placard" instead of "place card"?

Note that the encoder altitude displayed by the transponder will be pressure altitude (equivalent to a sensitive altimeter or QNH setting of 29.92/1013), rather than indicated altitude.


text:
Are there fees for international flights crossing through another country's airspace?
When an aircraft flies over another country are there fees associated with such flight? I am thinking particularly of international airline flights, though this might also apply to flights with the same country of origin and destination that transit another country's airspace.

Are there fees for flying through another country's airspace in general?
Are there fees for flying through the airspace associated with an airport in another country?

This is mentioned as part of the cost breakdown for a flight.

...but I think an answer to this question could add more specific detail than that related question.

I don't think that question adequately addresses this question; I don't find it to be a duplicate.

Related: http://aviation.stackexchange.com/questions/30125/how-does-a-national-atc-make-money

Most countries have implemented route charges billed to aircrafts overflying their territory and by doing so using their control infrastructure. Those fees are usually computed according the distance flown and aircraft weight, small aircrafts (eg. less than 2,000 kg in Europe) may be exempt. They are collected for every flight over the territory, both domestic and international.
In the same way, some countries charge terminal fees when the airport control infrastructure is used.
Those fees are most usually levied for flight performed according IFR (Instrument Flight Rules), not VFR (Visual Flight Rules).
In Europe, the EUROCONTROL organization is empowered by States to collect route charges and terminal fees.

For example, I flew right seat on an IFR flight through Niger airspace and we specifically avoided flying through Nigeria's airspace—even though this was out of our way—because that would have incurred user fees at the time. This was a 12+ years ago, so things may have changed since then.

here  is an example of the charges one has to pay to fly in Romanian airspace. Navigate to publications , AIP , AIP, open chapter GEN , section "Charges for Aerodromes/Heliports and Air Navigation Services" .

Including more detail from the link would make this answer more useful, especially if that link becomes inaccessible.

Unfortunately the romanian aip does not have permanent links. You should navigate to aisro.ro , select Publications / AIP and navigate to Gen 4 to see the charges.

In that case, that would be especially important to include that information in the answer, as well as the information at the link.

source: Stack Exchange

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text:
What are the advantages or disadvantages of a mid wing design?
Are there advantages or disadvantages to a mid wing design for a monoplane? If so, how would this design compare to a high wing or a low wing monoplane design?

What might be the aerodynamic advantages or disadvantages?
What might be the design or structural advantages or disadvantages?
What might be the control or flight characteristic advantages or disadvantages?

@JonathanWalters: E.g. De Havilland Vampire. Related: Aircraft Design: A Systems Engineering Approach (chapter 5, see 5.3.3)

Related: http://aviation.stackexchange.com/questions/701/what-are-the-pros-and-cons-of-high-wing-compared-to-low-wing-design

A mid wing design is mostly used on aerobatic and combat aircraft. The wing spar carry-through would be where the payload needs to be in transport and passenger aircraft, so a mid wing is the worst choice for these types of aircraft. When Boeing turned the B-29 into an airliner (the 377 Stratocruiser), they needed to add a second tube on top of the original fuselage, turning a mid-wing design into a low-wing.

Boeing 377 Stratocruiser (picture source)
Aerodynamic pros and cons

Pro: A mid wing position adds the least amount of interference drag. This is the main reason for using it on high-performance gliders.
Pro: Ground effect is less than for a low-wing layout …
Con: … but higher than for a high wing design.

Structural pros and cons

Pro: Puts the wing spar at the widest point of the fuselage cross section, so the load transfer is straightforward and the bulkheads can be lightweight, if no engines are in the way.
Pro: Leaves more space for wing-mounted ordnance or engines and allows a shorter fuselage-mounted landing gear …
Con: … but if the landing gear is wing-mounted, it needs to be longer and heavier than that of a low-wing configuration.
Con: In fighter jets with fuselage-mounted engines the air ducts and engines are in the way of the wing spar, so it needs to be built around the intake duct(s) and engine(s). This makes the bulkheads heavy.
Con: The spar will be where the payload needs to be in transport and passenger aircraft.

Flight characteristics pros and cons:

Pro: The inertial axes run through the center of the airplane, so any roll maneuvers can be performed quickly and without much change in the flight characteristics between upright and inverted flight. Note that most high-performance aerobatic airplanes use this layout.
Con: In single- and tandem seaters with a cockpit close to the CG the wing blocks much of the pilot's view in the lower forward region, which makes take-offs and especially landings harder.

Patty Wagstaff's Extra 300 over Florida (picture source).

The mid wing is mostly used in combat aircraft and rarely in passenger jets. The reasons are mostly structural.

Aerodynamically, the mid wing is the best option as it is much more streamlined and has less interference drag compared to the high and low wings.

The mid-wing also has neutral roll stability, which is good from the prespective of combat and aerobatic aircraft as it allows for the performance of rapid roll maneuvers with minimum yaw coupling.

The mid wing has certain disadvantages when it comes to structural design as far as passenger and cargo aircraft are concerned- the wing will have to either pass through the fuselage, eating into usable volume or the structure has to be strengthened around the fuselage to carry the loads. This is the main reason this type of wing is rarely found in commercial airliners.
There are some aircraft which do have mid mountedwings, like the Piaggio Avanti, which has the wings passing behind the cabin and canards and the Hansa jat, which solved the problem by sweeping the wings forward and thus passing it through the rear fuselage. These types are rare, however.

Image from hansajet.de
This type of wings are used by a number of combat aircraft, however, for example, the Dassault Rafale.

Image from http://indiandefence.com
For combat aircraft, the adoption of mid wings means that the landing gear have to retract into the fuselage for keeping the length under check. The mid wing allows for the carriage of weapons and fuel tanks in underwing pylons however. Also, the pilot's visibility is not affected during turns as in the case of high wing.

See also such aircraft as the F4-U Corsair and F4F Wildcat.

They have a main structural advantage:

Mid mounted wings have the advantage of being structurally efficient when aerospace engineers desire to incorporate a swept or tapered wing design on the aircraft. This increase in structural integrity is essential for aircraft that perform extreme maneuvers or aerobaticsSource: Student Pilot News

They also leave the aircraft free of spars on the belly and room for cargo. And they reduce the induced drag
The main disadvantage is the speed. The fastest planes use low-wings. Also many of this aircraft use spars in the middle of the fuselage, so you have to have a bigger fuselage and thus more weight.

It is aerodynamically the cleanest and most balanced, but the carry-through spar can reduce the useful fuselage volume near its centre of gravity, where space is often in most demand. It is common on high-performance types such as sailplanes.

A low wing allows the pilot to have a good visibility and a lighter structure because as it is below fuselage, it doesn't have to carry more weight. But there's also a main disadvantage which occurs when landing; it produces a strong ground effect compared to the high and mid-wing. In case of an emergency you can step out and can be used as overwing exits. And finally, they have better flexibility.
A high wing provides also good visibility and lateral stability. Also increases ground clearance for the engines and cargo.
More info can be found here and here.

Would it be possible for you to provide citations for your quotes?

How do I do that?

If you know where you found the quoted text, you can edit your answer to preferably add a link, or alternatively simply state where you found that information.

In my answer here you can see examples of what I mean. You don't have to do things the same way I do, it's just good practice to cite your sources.

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text:
Why did the space shuttle use bias-ply tyres instead of radials?
Aircraft and automobile tyres can be divided into two main types, based on the orientation of the tyres’ body plies (the layers of tough fabric that form the main structural body of the tyre); radial tyres are built with the body plies laid perpendicular to the bead and tread (so that the body plies extend straight out radially - hence the name - from the tyre bead, straight across from one side to the other at a 90º angle beneath the tread, and straight in radially to the bead on the other side of the tyre), while bias-ply (or simply bias) tyres have the body plies laid at an oblique angle.
Radial tyres are the more common type by far, for very good reason; they are stronger than bias-ply tyres and wear much more slowly.
I was, thus, rather surprised to learn that the tyres used on the space shuttle’s main landing gear were of the older, weaker bias-ply type:

Wheels and Tires
[...]
The main landing gear tires are 44.5 by 21 inches and have 16 cord layers in a bias-ply design. They are normally inflated with nitrogen to a pressure of 370 pounds per square inch (psi). The maximum allowable load per main landing gear tire is 132,000 pounds. With a 60/40 percent tire load distribution, the maximum tire load on a strut is 220,000 pounds. The main gear tires are rated at 225 knots maximum ground speed and have a life of one landing.  [Shuttle Crew Operations Manual; my emphasis.]

The space shuttle’s main landing gear would seem to be one of the worst possible places to use bias-plies instead of radials; with each tyre carrying up to 59.9 tonnes (66 short tons) and having to cope with touchdown speeds in excess of 200 knots, it would seem imperative to use the strongest tyres available.  The magnitude of the stresses placed on these tyres was so great that, while most aircraft tyres can make it through dozens to hundreds of flights before having to be changed, the shuttle MLG tyres were rated for a grand total of one use before replacement.  Additionally, with only four MLG wheels per shuttle orbiter, even a single MLG tyre failure would significantly impair the vehicle’s braking capability, which is most emphatically not a good thing for something going as fast as a landing shuttle orbiter.  Given all this, one would think that radial tyres would be the obvious choice, hands down, for the shuttle’s main landing gear, since their greater strength and slower wear would considerably decrease the chance of a tyre failure upon landing - yet the shuttles instead used bias-ply tyres.  Why?

I am going to go out on a limb and suggest that the tires are only used once, also they may have taken weight into consideration and if a blow out, the steel shrapnel? Just a thought.

It's worth noting that most aircraft tires were bias-ply during the shuttle era. It's only in recent years that radials have started to be common on airliners, like the Boeing 787 or Airbus A350.

@Bret Copeland is this do to FAA being slow to adopt?

This would be better asked on Space.SE.

It's interesting to see that NASA got realistic on tire life. When I worked on the Shuttle in the mid '80s, the tire life was molded into the sidewalls as 'Good for 6 landings'. They were never used for more than one landing. It was obvious from one look at the tires after a landing that they were done.

The natural advantage of radial tires is their behaviour when making turns and when rolling on very uneven surfaces.  Neither of these is a significant factor for shuttle landings.  So the real question to answer is, why would anyone ever want to use radial tires for the shuttle?

@RayButterworth: Radials also have a natural advantage in their greater strength, lower heat generation, and slower wear, all of which reduce the risk of tyre bursts during landing - something which very much was a significant factor for shuttle landings.

@Sean I daresay the heat&war generated by the slip at touchdown, which isn't really any different between radial and bias, completely dwarfs what happens in the short rolling phase afterwards. Not to mention that the tires receive a lot more heat from the brakes than they would in automotive application; again, radial design doesn't help with this.

I'm intrigued: were the wheels used for breaking at all on the shuttles, or was it almost entirely the parachute?

Simply put, for the weight bearing factor bias-ply is a lighter tire, and when building a spaceship weight is the top concern.
The reason they were thin and single use also had to do with weight, according to NASA:

Weight: Since weight is of extreme importance, the tires are made with
  a minimum amount of tread to conserve weight, allowing for larger
  payloads. A few pounds may not seem to make much difference, but when
  you add up all of the ways to decrease weight throughout the shuttle
  it can have a significant impact.

When it comes to weight bearing capacity:

Load-Carrying Capacity
Advantage: Bias Ply
Due to their multiple layers, bias ply tires generally have the
  advantage when it comes to load-carrying capacity. Because there are a
  uniform number of plies to support the weight of a vehicle in both the
  tread face and the sidewall, bias ply tires are generally better when
  hauling heavy loads. This is why trailer tires, tractor tires, and
  heavy equipment tires are often bias ply; they can better support
  heavy loads. Radials are available with high load ratings, but the
  weight-carrying capacity requires adding many more plies to a radial
  tire, making them very stiff.

The important line here being "adding many more plies" which will also make the tire heavier (reference above note on weight). It costs in the neighborhood of $10,000 to put 1 lb into space, so if you can save a few pounds on each tire, it does not matter that they cost \$5,660 each; you save by replacing them every time if they are indeed lighter.

even a single MLG tyre failure would significantly impair the vehicle’s braking capability, which is most emphatically not a good
  thing for something going as fast as a landing shuttle orbiter.

The shuttle has no issue coming to a full stop with a blowout as was the case with the shuttle Discovery in 1985 during the landing of STS-51-D.

Re: STS-51-D, Discovery had the advantage of being able to use one of the longest runways anywhere in the world (and most of the ones that are longer than the SLF's runway are like that as a consequence of being at high-altitude airports), and, even so, NASA considered the risk from tyre bursts and/or brake failures during a landing at KSC to be so severe that they shifted the next eight flights to land at Edwards instead while they modified the orbiters to increase safety during landing.  Also, what if a shuttle had had to abort during ascent (or make an unplanned emergency deorbit)...

... and land heavy at an emergency site, with a shorter runway than the primary landing sites, and lose one or more tyres during a heavy, fast landing on a (relatively) short runway, and go off the end or side of said runway due to the resultant loss of braking force?  And, finally, given how much weight they managed to shave off the shuttles over the course of the programme through various improvements, I have difficulty believing that they wouldn't be able to compensate for heavier radial tyres by finding a way to trim weight somewhere else.

@Sean, most of the emergency landing sites had runways of at least 11,000 feet, with 12,000+ being common.  (And one of the post-Challenger enhancements was a braking parachute, which presumably weighs less than better tires while providing benefits in more situations.)

@Sean the likely could have accounted for the increased weight of a radial but chose not to since they could sell that payload space to customers instead. Radial tires are not necessarily stronger so there is no need to lug the weight around.

Also, the sidewalls of a bias-ply tyre give and absorb a lot of the shock.

@Vikki " I have difficulty believing that they wouldn't be able to compensate for heavier radial tyres by finding a way to trim weight somewhere else. " What I have difficulty believing is that some self-appointed armchair expert on the internet is better able to judge the tradeoffs than the engineers who designed the Shuttle.

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text:
How do active blades work on helicopters?
Can someone throw some light on 'active blades' as used in helicopters? I'm mostly interested in the use of piezoelectric material and actuators.
How are the actuators able to sense the change of aerodynamic forces on the blade?
 What is the subsequent action of the actuators which results in a reduction of noise level of the rotor?

Do you mean to ask how the rotor blades are chamging their angle of attack?

The idea is to have flaps on the trailing edge, moved by piezoelectric actuators or benders within the blade, which displacement is mechanically amplified. The flaps change the airfoil to cancel blade vibrations (e.g. by twisting the blade). A variation is to deform the whole width of the blade. The principle of a piezoelectric material is it changes its length when an electric field is applied on its faces (and vice-versa). This article seems interesting.

This should answer your question:
https://www.icas.org/ICAS_ARCHIVE/ICAS2008/PAPERS/842.PDF

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text:
Do I have to notify someone or file a flight plan for a private flight in the UK?
Say I have a private pilot's licence (PPL) and I want to go on a flight, say from Stapleford (ICAO: EGSG) to Damyns Hall Aerodrome (ICAO: EGML). What would be the procedure for the journey i.e. would I have to notify anyone or submit a flight plan to the CAA?

Stapleford and Damyns Hall are both in class G airspace, so there would be no need to file a flight plan or ask permission of anyone to make the flight. The only thing you might need to do is call Damyns Hall in case they are PPR (Prior Permission Required). VFR flights generally don't need any sort of flight plan unless you are going abroad or to the channel islands. If you are going a long distance over water it's advisable as well. If flying into Damyns Hall keep in mind that the London City zone is very close by, so make sure you stay clear of it. The London TMA is at 2,500ft as well.
Both airfields are not controlled, however both have AG radios who try to coordinate flights, you technically don't have to communicate with them but you might not be allowed to use those airfields in the future if you don't use it.


text:
How different is flying through Free Route Airspace (FRA)?
I understand the flight planning and ATC aspects of Free Route Airspace. I'm trying to understand what a pilot does differently while flying in an FRA. Are there changes to standard procedures while transitioning from ATS routes to FRAs and vice-versa?
How does the pilot handle deviations/re-routing from a planned route (typically a straight line between the chosen Entry and Exit points), especially when this can pose risks of conflicting with routes of other aircraft flying in the FRA?

Short answer: We do nothing differently in the cockpit when flying in a FRA. The route segments are filed as a long direct and simply flown like that.
As ususal conflict prevention/solving lies with the controller. Only short term conflict solving lies with the cockpit crew (think TCAS RA). In a FRA this is nothing different. In a "regular" airspace with airways and waypoints the problem is the same. Only are your conflict hotspots concentrated on waypoints where you have crossing or converging airways.  This presents similar problems to the controller.
The FRA I mostly fly through is in south-east Europe (Vienna, Ljubljana, Bratislava and Budapest FIRs). Often the Austrian controller clears us from our western entry point on a direct all the way to the eastern exit point of the adjacent Budapest FIR. So there is some trans-national coordination going on in the background.
From the Eurocontrol Free Route Airspace FAQs:

Have ANSPs developed strategies to mitigate the potentially more
difficult detection of conflicts that comes with FRA implementation?
[...] ATC systems across Europe [...] include conflict detection tools
[...] using aircraft trajectories calculated by the ground system which
are updated in real time as a flight progresses.  [...]  The tools help
controllers identify conflicts well in advance of them occurring [...].
At the same time, the implementation of Free Route Airspace generates a
much better spread of conflicts compared to the concentration of
conflicts generated by the fixed route network.

source: http://www.eurocontrol.int/articles/free-route-airspace, omissions by me
Route deviations from cockpit side (to avoid weather for example) are handled like everywhere else. Ask the controller for an avoidance heading and you're good to go. Possible arising conflicts are then solved by the controller. Same works for conflict mitigation from controller side. You might get a heading until clear of conflicting traffic and then a direct clearance again.
In my experience this works just fine in the daily operation.


text:
Are there any apps for easy Part 135 Flight Time and Duty Period calculations?
I need a solution to quickly and easily assist me in calculating Part 135 duty time.
I am a charter broker and presently use estimations for my own consideration, but rely on advice from operators to provide informed consultation to clients.
It takes me too long to arrive at my own estimations, and I feel like there would be a tool out there designed to save me time. I saw a couple of apps in the App Store, but I wasn't impressed and would like your opinions.

It doesn't have to be an app either. If there are websites people use for this, open to give it a try, as well as consider any other tools recommended to help me be more efficient and informed. *It is possible that I am just not educated on the variables enough to effectively use the apps that I found. I have never had any formal flight training. I'm no Pilot and have never worked for a charter Operator. However, I do have a long background in aviation and know a thing or two. Learning more every day! Thanks for your help :)

Welcome to aviation.SE! We generally don't answer resource location ('shopping') questions because there are too many variables and opinions, and apps come and go all the time. Having said that, I know very little about part 135 and perhaps there's a de facto standard tool out there. If you don't get a useful answer here, you might get a better response in a discussion forum.


text:
Why did Boeing remove the engine chevrons on the 777-X?

From the most recent renderings on Boeing's site, it looks like the engine chevrons found on the 787, 747-8 and 737-Max have been removed from the 777-X. Is there a good reason for this?


text:
What is the call for when an enemy air-to-air missile has been fired?
In a scenario where a large multi-crewed aircraft was being attacked by a fighter that launched an air-to-air missile what would the call be that would alert the pilot that a missile was in the air and potentially tracking them.  I know the term 'Rifle' but I always assumed that meant a friendly missile in the air, is there a specific call for an enemy missile?
Also is there a call for a SAM launch?

Any particular country?

Ideally the USA

"Get me out of here"

Have you read the Wiki?

I did but there didn't seem to be an air-to-air missile specific entry

Is there a reason that you didn't ask for the Russian version of this?

"Oh Sh!!!t"   or a variation thereof.

From an older NATO book on brevity words that I have, a hostile guided missile is VAMPIRE.
A hostile surface to air missile is, indeed, SAM.
Edit.
From the better list of brevity words
VAMPIRE  Hostile anti-ship missile

So VAMPIRE is not an air to air missile.
My old list did not specify the type of the hostile missile.

As I recall, that was for surface to surface missiles.  (But it's been three decades since I had all of those memorized, so don't take that as gospel).

Link to brevity codes

A vampire is the term for an incoming anti-ship missile, not an air to air missile or ground attack missile.

When you see an enemy missile or its smoketrail you call out SLAMEYE with your position and the direction to the missile.
For hostile cruise missile launch its QUAIL.
Hostile radar lock on you is called out as SPIKED.
For example: SPIKED 4 o'clock

Could you provide sources for these?

https://www.scribd.com/document/167065842/Joint-Brevity-Words-Publication-App-07e

Your article is behind a paywall on a website selling documents it doesn't have resale rights for, aka piracy and intellectual property theft.


text:
Is ADS-B UAT required below 18,000 ft for ADS-B ES equipped aircraft?
If an aircraft is flying in the USA with 1090 MHz Extended Squitter (ES) and it is below 18,000 feet, does it then need to also have 978 MHZ Universal Access Transceiver (UAT) so that aircraft flying below 18,000 equipped with 978 MHz (UAT) can detect it?

From Wikipedia: "UAT users [...] can receive reports from proximate traffic (TIS-B) through a multilink gateway service that provides ADS-B reports for 1090ES-equipped aircraft and non-ADS-B equipped radar traffic. [...] Viable ADS-B UAT networks are being installed as part of the United States' NextGen air traffic system."

No. ADS-B ES equipped aircraft do not have to have UAT to allow ADS-B UAT equipped aircraft to 'see' them. Below FL180, they are tracked by ATC radar and their track is translated and re-transmitted to UAT equipped aircraft via TIS-B service. More information, as well as coverage maps are available at the NextGen ADS-B site.

Actually, aircraft broadcasting ADS-B Out on one frequency (say 1090Mhz) and equipped with ADS-B In, will receive traffic operating ADS-B Out on the other frequency (in this example, 978Mhz) via the ADS-R (ADS-B Re-broadcast) service.


text:
Gliding range if engine is off
The engine was turned off at 1000m above sea level. If you ignore the landing pattern, how long can the runway be within a few kilometers of the landing to safely land? However, the wind is blowing at 72 km / h from behind.

Empty weight = 90kg, fuel = 30kg
zero lift drag coefficient = 0.05
Oswald = 0.75
Span 4.5 m
Wing w Area 3.7m^2
Cl =0.1(alpha + 1)

I am really confused if the wind is blew from head or tail how it influence on range.

The influence of the wind is very important in what concerns range. For example, if you're gliding with a headwind (measured, as all winds, with respect to the ground) that has the same speed as the airspeed measured by your anemometer on board the aircraft, the descent trajectory will be vertical, and the range will be zero...

The distance of the glide is computed, from the L/D ratio, related to the air mass. If the air mass moves related to the ground, the ground distance is changed according to the air mass speed. If you walk 10 meters in 10 seconds in a moving train, the actual ground distance depends on the train move during this time.

I'm not sure if you're asking a) how to calculate gliding range, or b) how wind affects gliding range. The second question is probably answered here.

I am appreciate to your answers. Then, what I really want to know is first question. Even though, now l start to understand gliding little bit thank you

You do have everything needed to calculate the aircraft's L/D and best glide speed (assuming you $c_{d_0}$ is referenced to wing area too, because you don't have frontal area), but it's somewhat more math.

I'm going to assume that when you say 1000 meters above sea level, what you really mean is 1000 meters above ground level. 1000 m AMSL can be underground in many locations.
First, you need to understand that the airplane, once in the air, always moves together with the surrounding air. The surrounding air can be moving relative to the ground – what's usually referred to as wind – but assuming sufficient altitude above local ground, the airplane is largely unconcerned with what the ground is doing under it.
Second, every airplane has some glide ratio. The glide ratio tells you, for each amount of distance covered, how much altitude you will lose. Typical values for light motor fixed-wing airplanes might be around 10:1 to 12:1, while commercial airliners might get 15:1 to 20:1, and high-performance gliders can exceed 50:1. For simplicity, I'll assume a glide ratio of 10:1, which is pessimistic, but which should be achievable by most light motor airplanes. (User XRF pointed out in a comment that these values might actually be on the optimistic side, but I'm sticking with them because the point is to illustrate the principle, not to give an exact calculation.)
Typically, the glide ratio is quoted at speed and configuration of best glide, so your first course of action when losing the engine should be to configure the airplane for best glide, and re-trim to match.
What the 10:1 tells us is that, for each 1*X meters (or feet) of altitude that you lose in a glide, you will cover 10*X meters (or feet) of distance. Since you start out at 1000 meters above ground, this means that you can cover 10*1000 meters or 10 km of distance before your flight path intersects ground.
However, again, that's distance covered through the surrounding air mass.
To figure out how far you can travel along your ground track, you need to figure out the amount of time for which you can remain in the air. Let's say that the speed of best glide in your airplane is 100 km/h indicated airspeed. Since you can travel 10 km through the surrounding air mass, this means that your travel time after losing the engine is 10/100 of an hour, or six minutes.
In six minutes, the 72 km/h wind will push your airplane 7.2 km along the ground, because six minutes is 1/10 of an hour, and 1/10 * 72 = 7.2.
Therefore, if you maintain that tailwind, with this highly simplified example, the point where you reach ground level will be 7.2 + 6 = 13.2 km from where you lost engine power.
If you instead make a 180° turn to head straight into the wind, you now have a 72 km/h headwind and a 100 km/h  indicated airspeed, for a ground speed of 100-72 = 28 km/h. You can still travel 10 km through the airmass before you reach the ground, and this still takes 6 minutes, but in those 6 minutes, your ground track distance is only 2.8 km.
The major advantage of turning into the wind is that when you reach ground, you will do so at a relative speed of 28 km/h, rather than 172 km/h, assuming an unchanged 100 km/h indicated airspeed. (This is why you always land into the wind.)
Therefore, with that wind, depending on which direction you turn into, your point of contact with ground, with these assumptions, will be somewhere between 2.8 km from where you lose engine power, and 13.2 km from where you lose engine power, expressed in terms of ground track distance.
In practice, however, if you lose the engine while in the air, this is all awfully academic. Rather, you'd pick out a nearby spot on the ground that looks reasonably even, level, and large enough to set down on; and head that way. There are virtually always ways to lose altitude, but without engines in an airplane not designed as a glider, very few ways to gain altitude. With experience, you might be able to quickly judge if you'll make it to the runway or not; but any controlled landing, even an outfield landing, is always better than a crash. You can always worry about getting the airplane back to the airport once you're safely on the ground.

Of course, covering 10Km of ground (as in your example) requires that the ground cooperates and remains level. If it should chose to rise up in front of you, you'll meet it much sooner.

@FreeMan For the sake of simplicity, in true physics textbook fashion, I assumed a perfectly flat ground of infinite extent. I also assumed some other things, including the pilot immediately attaining speed of best glide, that all turns are absolutely perfectly coordinated, that the pilot remains calm throughout the entire exercise, and so on.

I believe the data given in the OP‘s question is sufficient to calculate best glide speed and achievable glide ratio for the given scenario when assuming quadratic drag polar (I am not in a position to try myself for the next couple of hours hence just very lazily commenting...). I also believe, looking at weights in original question, there won’t be a (human) pilot on board.

I think your glide ratio's are a little optimistic. A Cessna 172 does about 7:1, a DA-20 that was designed from a motor glider does 14:1. The "Gimli Glider", a Boeing 767 that ran out of fuel managed 12:1. While the best open class sailplanes can manage over 60:1, most gliders are in the 30:1 or 40:1 range.

"1000 m AMSL can be underground in many locations": The only place reaching -1000m MSL seems to be in Antarctica.


text:
Does the pilot still have final control authority on modern Boeing airplanes?
In this answer it is said that Boeing (contrary to Airbus) gives final authority to pilots, but the example is about a 747-100(SP). This answer states, that modern Boeings have have a lot of fly-by-wire systems too. After reading over 10 (I think) Aviation.SE questions about the B737Max and MCAS it got me wondering.

How much authority does the pilot have or can the pilot get in modern Boeing planes? (as in how much does fly-by-wire/other electronics involved ignore/adjust/overrule pilot input (or independent commands) in each mode or law.)
Is there a difference between models? (for example 747-8i vs 787)
And how do the laws switch on their on vs pilot forced?

Disclaimers:
I am not interested what you think is better or are used to, or design philosophy, or stick vs control column.
I appreciate data about 737NG too but consider it an "old" model.
I am interested in 777X too but unsure how much definitive data there is.
Correct me if I got my facts wrong and please be gentle, I am a noob.

I think you fell for a common misunderstanding:
Fly by wire ≠ flight control augmentation
It is - in the first place - another method to get the pilots input out to the control surface just like cables or pushrods. Just not mechanical but electric/digital.
If you want to alter the pilot input for whatever reason it is way easier with digital signals then with a mechanical input.
Example: The speed brake in an A320 vs in a B747. If you rapidly extend the speed brake in an A320 aircraft, the extension rate is limited by a computer making for a smooth movement of the control surface. If you do the same in a B747 the system tries to match the lever position as fast as possible with all available hydraulic power (3000 psi). So rip on the speed brake lever in a B747 and the heavy aircraft will jolt quite a bit.
Concerning flight control augmentation it really boils down to the design philosophy. In a B747 you can do basically whatever you want (even stalling) but in the B747-8 you have some systems augmenting pilots input. Tail strike prevention on rotation and the nose down trim when flying a flaps 30 approach come to mind. I can't speak for the B787 but the B747-8 is, despite its largely fly-by-wire architecture, still a conventional airplane with (almost) full control authority by the pilots.
The B777 family brings flight control augmentation to the table where the computer shows you the limits via the control forces generated in the control column. The computer shows you where it thinks you should stop but if you decide to press on you just have to double the force exerted on the control column and the aircraft will do what you want.
The Skybrary has a good primer article on flight control laws for both Airbus and Boeing designs. It gives a good overview about the similarities and the differences in design and philosophy. Shoutout to user Simon Opit who brought it up.


text:
Will an axial compressor work with an ideal fluid?
Will an axial compressor, like the one described starting on page 275 of Mechanics and Thermodyanmics (PDF link), work if the flow was assumed to be ideal (i.e. incompressible and inviscid)?
Specifically, what mechanism will slow the flow down in the axial direction? It's my understanding that slowing the flow down is the job of the stators, but I fail to see how they accomplish this in the axial direction.  The author states on page 284 that the axial flow velocity through the compressor is made constant by design but never explains how that design is achieved and I'm curious if that design could still be achieved with an incompressible fluid. -Thanks in advance!

Are you asking mathematically or physically?

I'm wondering what a compressor might do with an incompressible fluid?

@JZYL, I think I'm looking for more of a physical explanation based on the math (i.e. an incompressible fluid is not physically possible so the mathematical assumptions must be considered)

@Haukinger, haha I see the seeming paradox, you cannot compress a fluid by increasing it's density (because it's incompressible), but you can increase it's pressure. I guess my question is trying to determine whether a compressor would work on a fluid like water (essentially incompressible).

Yes, you can axially compress water: https://en.wikipedia.org/wiki/Axial-flow_pump

@JZYL, the rotor blades will create downwash in the radial and axial direction. The radial component is removed ("diffused") by the stators. What removes the axial component? Maybe conservation of mass handles this naturally...?

(Figure 7.7) The angle of the blades gets steeper across the direction of flow (beta angle). The fluid travels slower and slower as it goes through the blade due to this steeping angle (velocity w). Remember velocity of the fluid is not parallel to the axis but perpendicular to the velocity of the blade (c is constant but w isn't). You should read this chapter thoroughly.

@user3528438, thank you for the comment. If you look at Figure 7.8, you can see that the axial flow velocity ($c_z$) is assumed to be constant (at least pictorially), and is therefore assumed to not slow down. Also, I'm not understanding why your saying c is constant as $c_1\ne c_2$.

First of all, incompressible flow is subsonic, however subsonic flows are not all incompressible. An ideal gas flow may be "incompressible" until it meets the compressor. Even if the vehicle is travelling at supersonic speed, the flow is reduced to subsonic ("incompressible") flow by the intake system before reaching the compressor. At this point the subsonic flow gets compressed. Presumably this is what is meant here.
The compressor stages each reduce the cross-sectional area, while the fans draw the gas backwards to maintain velocity. Thus the gas, ideal or not, must compress to fit the reduced volume available to it. This compression creates heat which raises the gas temperature, further raising its pressure.
Viscosity is necessary to establish a circulatory flow component around each airfoil-shaped blade (the Kutta condition). It is this circulatory component which creates the velocity differentials needed for the Bernoulli principle to create the dynamic pressure differentials which make the blades do their work. Superfluid helium (close to absolute zero) has no viscosity and has been found to exert neither lift nor drag on an immersed body.

Incompressible flow is subsonic. Subsonic flows are not all incompressible...


text:
How is fuel managed in the Zero-G A310?
There are several Zero-G airplanes to experiment briefly microgravity without going into orbit. One is the A310 from Novespace (F-WNOV):

Novespace A310 F-WNOV (source: Jonas Wirz at Airplane-Pictures.net)
When a Zero-G flight is executed, fuel should take the form of a sphere in the tanks, like demonstrated in the cabin for a beverage.

Advertisement in microgravity (source)
Thoughts:

This effect won't appear in negative G, subject to the design, fuel lines may still be immersed in tanks, this cannot be the case in micro-gravity.
The 0G segment is likely flown with power. First this is not a continuously descending flight as seen below. Second, friction will slow down the free fall anyway and must be compensated by some acceleration from the engines.

0G segment is not limited to the descent (based on source)

How does Airbus ensure the fuel is still delivered to the engines at the required pressure, without air?

Related: Are engines fed differently in reduced gravity aircraft?
Basically it says no modification is required because the lines are pressurized, and this is supported by a 1966 Nasa study (Use of aircraft for zero-gravity environment) which is not more detailed. The line being pressurized downstream of the pumps seems only one element of an adequate design. Upstream fuel will experiment the effect of micro-gravity and lines are no more immersed in the fuel. Air can enter and create a problem when reaching a pump or an engine. Pumps could be drained. Maybe the problem won't appear during the 0G segment, but it should appear later.
I'd like to have the details about how pumps, pressure, flow, or anything else contribute to maintain a good fuel supply to the engines.

This is the fuel system for the A310:

(Source)

An A310 uses 730lbs/hr in idle descent which equates to 117 gallons per hour. That's 2 gallons per minute. Since Zero-G only lasts 22 seconds, it only burns 0.75 gallons of fuel. I'm sure that there is enough in the lines to accommodate 22 seconds without starvation.

If it were that much of an issue, fighter jets would experience fuel starvation pretty often while executing zero-g and negative-g manuevers. ;-)

@DevSolar Fighter jets are designed to perform those kinds of maneuvers and have specially designed fuel systems to keep that from happening.

I'm not an expert in this field, but I do know that at least some aerobatic/fighter aircraft have an auxiliary tank that holds fuel to extend the time the plane can fly inverted. I suppose once the aircraft returns to upright mode, the inverted tank is refilled.

@RonBeyer, since Novespace flies their A310 specifically for the parabolic micro-G flights, they may well have modified the fuel systems to accommodate the expected flight regime.

@RonBeyer: Good point if the parabolic path doesn't require thrust. I wonder if it's the case due to air viscosity. Is it possible to have pumps and circuitry empty for 22 seconds, and then fully operational for climbing at the end?

A pressurized bladder tank would be an obvious solution, but I don't know if that's the actual answer.

Seems like a dupe of this question: Are engines fed differently in reduced gravity aircraft?

@mins consider edit your question to emphasize both questions are different.

@ManuH: Done. Thanks for the suggestion.

I wrote an email to AirZeroG and asked them:

Other than the interior, are your aircraft modified in any way to handle zero-g flight?

Here is the response that they gave me:

Dear Sir,
Except free floating area cabin configuration, there are very few differences with a “standard aircraft”. The most significant one is installation of Zero-G meters in cockpit and a very simple installation on the wheels to help one pilot to lead the aircraft only in vertical axis, and the other pilot to lead only in horizontal axis.
Out of that, the biggest difference is maintenance program: each parabola performed to create Zero G onboard is considered as an aircraft cycle for the aircraft and its engines, and maintenance adjusted accordingly. Such consideration dramatically increases maintenance costs of the aircraft.
Kind regards
Gilles GOMPERTZ

I would say that if there were a fuel system difference they would say that is more significant than G-Meters in the cockpit. I'm assuming based on the response above that the fuel storage/delivery system is unmodified.

You deserve the bounty for the extra mile! +1

With @TomMcW! Thanks a lot. Someone may later provide additional factual explanations about the procedure used or figures showing how this is possible with the unmodified fuel system. Anyway Ron this is a great idea of yours :-) I appreciate.

That's pretty wild about the split controls. I guess with people floating around loose in back you'd have to fly that parabola pretty precisely. Wouldn't take much to slam them into the walls

I agree, @TomMcW. I'm not a pilot, but I'd imagine this would be similar to driving a car with one person steering and another working the gas/brakes. I wonder if the control split is only during the 0G segment or if it's a full-time engagement. That would make for some interesting landings until both pilots really got the hang of things!

@FreeMan would make it interesting indeed. With all the duties the PNF performs during approach and landing he needs his hands and attention free so I'd bet it's something that can be disconnected quickly after they finish the aerobatics. Might even just be some kind of handle that allows one of them to operate the yoke without holding the wheel

Jet powered aircraft use feeder tanks to stabilize the flow of fuel to engines and APUs.  These feeder tanks are pressurized and kept full to a specific amount to ensure fuel flow (for a certain period of time).  The feeder tanks are fed by a system of transfer pumps from the main tanks, which in turn are pressurized (usually with an inert gas mixture).  Unlike most gravity fed tanks, the tank is not drained via a single sump type arrangement, but a more complicated series of apertures for fuel to flow into the feeder (which may include in tank pumps).
While I cannot speak exactly to this aircraft, it is usually the case that special mission aircraft have fuel systems modified or designed to suit their needs.  This aircraft may have a larger feeder tank or a different feeder tank design that allows for extended periods of low-g operation.  Generally speaking, low-g operation does not have an affect on pressurized fuel systems.
Much of the information you seek is provided by the FAA here:
https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_ch14.pdf

Thanks for the answer, however this is a general one without actual details. Here is the fuel system for an unmodified A310, and this extract for the schematics. Could you please explain using these elements?

@mins, now I am curious.  The schematics you have clearly indicate that they are using isolatable wing and center tanks, each with independent pressurization and pumping sources.  What are you looking to understand?  Is it the position of the pumps/sumps in the tank relative to the liquid fuel?  Take a look at the document you posted, it shows the use of baffles to restrict fuel movement, which prevents completely unconstrained movement (as shown in your picture).

"it shows the use of baffles". I don't see baffles mentioned, what page? I don't see how baffles prevent the possible 0G starvation (in addition I imagine the tanks would be far from full for the 0G short flight). "they are using isolatable wing and center tanks": Again I don't understand whether you suggest the isolation valves are closed or left open during the 0G segment? Don't you want to include the pertinent elements from the schematics in the answer to clarify? Thanks.

Baffles reference: 1.11.20, P.1, GENERAL.  Baffles will reduce the fuel's ability to flow unconstrained, and as such will prevent it from forming its lowest energy state (a spheroid).  They are there to prevent slosh, and will be more effective at preventing spanwise flow than chordwise, but will still have some value.  0G starvation is prevented by the pump being immersed in the fuel, or by using immersion lines.  Without seeing the lines, it is not possible to know the mounting (nor will the general A310 fuel system design give you the answer if the 0G aircraft has been modified).

Ok for the baffles. I'm less sure they would be sufficient to prevent fuel from leaving the pump inlets exposed, with the risk of air entering the line, causing problems during, or maybe after, the 0G segment. About the isolation valves you mentioned earlier, should they be closed or open?

The isolation valves let you isolate the wing tanks from the center tank. If the center tank was less than full and the wing tanks were full, then closing the valves would also help offset g effects. Largely, they wouldn't matter because the center tank would be pressurized to prevent fuel back flow.


text:
Is there a way to fly an UAV over a roadway?
With an FAA Section 333 Exemption, they will permit you to fly up to 400' above ground level. But they also restrict you to flying at least 500' away from people and vehicles unless you have their permission. You can't get permission from every vehicle driver that happens to be passing by. Does this effectively mean that there is absolutely no way to fly over a public roadway, or is there another exception or reasoning to be able to do this?

Wait for traffic to die down? (Depends on the roadway, of course...)

The regulations are put in place to protect the people on the ground. Consider what can happen if your UAV became uncontrollable - loss of power, impact with power lines, a bird, etc - and impacted the roadway or a car. You could cause a major accident. Your drone causes a car traveling 30 MPH to swerve into a telephone pole, killing the driver or a pedestrian. Do you want to take that risk? I think that is the real question, not how to get an exemption.

For certain operations the FAA does grant waivers to 14 CFR § 91.119(b) and/or (c). These waivers are generally granted for the purpose of allowing pipeline or powerline patrol, aerial survey, or for other operations that are in the public interest. The waivers are also generally granted to the operators of certified or restricted category aircraft, not UAS.
If you represent an operation for which a waiver would be in the public's interest and can demonstrate that the operation would be conducted safely, you might qualify for a waiver.
However, even for that waiver, you have to demonstrate strong evidence to gain a minimum distance of less than 500 feet:

3-185 A. Unless it is necessary to
  safeguard human life or it can be determined to be in the public interest and contributing to the public health, welfare, and safety, the 500-foot minimum separation distance from persons on the surface shall not be waived.

Note that 14 CFR § 91.119(a) and (d) are never to be waived.
See this document for more information on the above discussed waiver.

Now, all that being said, I don't know if the above example of a waiver apples directly to your question or not; perhaps 91.119 is not the regulation that you were concerned about. Regardless, that waiver is an example of what can be worked out.
The current UAS issue is uncharted water for the FAA; there may or may not be precedent for an operation or exemption. Bottom line, if you have a really good reason to do the operation you want to do, you might be able to work it out with the FAA. Otherwise, you will have to stick to the rules as they are.


text:
What do airline pilots eat on a flight, and when?

Do airline pilots eat while flying or do they wait until they are back on the ground?
If they do eat, do they get the same food that is served to the passengers or do they bring their own meal?

Related

I'm surprised that people have voted to close this question as a dupe of the different meals question. They're asking different things.

@Pondlife I agree that they are different questions, the only similarity is the meal pilots eat.

1: Do pilots eat during flight or they wait until they are back on the ground?
As pilots happen to be humans, their metabolism works in a similar fashion as yours or mine work. So they eat when they are hungry. On a long flight, they can eat during the flight, but on short flights (e.g. 30 minutes - 2 hours), they might not get enough free time to have a meal.
On busy days, pilots may not get enough time to have proper meals, so they try to eat small meals containing more nutrition. This is detailed in an article on Airline Pilot Central. They also avoid heavy meals before a flight.
2: Do they get the same food that is served to the passengers or do they bring their own meal?
Most of the time, food served to the passengers is the same which is served to the pilots, although they don't eat the exact same food. An airline pilot revealed that:

... the pilot gets the first class meal and the copilot the business
  class meal.

Does the whole crew eat at the same time or do they stagger it?

@ToddWilcox They all go to the dining area where they've a big large round table, the captain says the grace and they all thank the Lord for the food. It's normally a multicourse meal, which can last 1-2 hours. Oh wait, we are on a flying airplane. Forget all that, the primary focus always is flying the plane, reaching the destination and serving the passengers.

I laughed. And still don't know what I was curious about. But I did laugh. :)

@ToddWilcox: One pilot always has to be watching instruments in case something goes wrong and pay attention to ATC, so they should stagger it.

I add: (1) only during cruise (2) eschew candy, personally. (3) Our regulations required the pilots to eat different meals. (4) by "watching instruments" necessarily means not eating. As a practical matter, one cannot be in control with a meal spread across his lap.

I thought that that was what the fancy tray table on Airbus airplanes was for.

I wonder if the avionics is resistant to hot coffee. Hmmm.....maybe that needs a question of its own. :)

curious_cat - no, they aren't, and the question already exists ;) http://aviation.stackexchange.com/questions/13534/are-the-buttons-switches-in-the-cockpit-spill-proof

Having had a 30 year career as an airline pilot I could probably answer this question.  Back when Airlines were still traditionalist in the 70's and 80's, our Airline had no restriction on what or when we ate.  Though not put on board especially for us there were usually enough meals left over that we got passenger meals.  (Though the Flight Attendants often would eat the first class meals and tell us that all was left were coach meals.  They thought we believed that).
Early 90's we got box lunches, not great but OK, better than airport junk food.  As we moved forward the into the millennium we didn't get anything other than peanuts and snacks as that was all was on board as domestic airlines cut out passenger meals.  We were reduced to getting airport food, and unless we had a long layover between flights it was quick stuff you could get in the concourse, like cholesterol laden hot dogs etc.
As for time to eat, usually it depended on when you got served: a flight of an hour or less you probably ate it after you landed and where parked at the gate.

One quick story about first Class meals.
I was flying a transcontinental flight to San Francisco from the East Coast.  For some reason only known to the Flight Attendant Scheduling Gods, all 5 of my Flight Attendants were new hires on their first trip. True to form the #1 flight attendant announced to us that First Class passengers had all requested their meals and the crew was gonna have to settle for coach meals. After we had eaten I got up and went to the cabin, opened the Curtain to the forward Galley and there were two flight attendants shoveling down Lobster from first class meals as hard as the could go.  The poor #1 when she saw me damn near choked on hers.  I didn't get upset though, those first year Flight Attendants made salvation wages while on probation many living 5 and 6 in a two bedroom apartment to make ends meet.  So much for the myth that the Captain got his choice of the meals.


text:
What might have been the reasons for this low flight altitude?
I was flying from Heathrow to Miami last wednesday (AA 39) and for the first ⅔ of the flight we were flying at 28.000 feet, only afterwards did it go up to 33.000 feet. So far I was under the impression that for reasons of fuel efficiency, airliners would try to fly as high as possible, and looking at the same flight on different days, it seems like they do in fact usually fly higher. So what could have been the reason for such a low altitude? Was it just weight due to being fully loaded, or are there other reasons as well?

Weight shouldn't be a factor; you were on a 777-300ER, and would have had plenty of engine power to maintain whatever altitude you wanted.

Looking at the route your plane took, this low altitude flight was likely to avoid the polar jetstream. This is a band of wind that blows west to east in roughly the area the first half of your flight was flying through. It exists mostly between 30,000 and 39,000 feet altitude, and can range from about 60mph to over 200mph. I suspect that the low altitude was to keep the plane below this jetstream, avoiding the headwind and fuel and time costs that flying through it would create. To answer the other part of your question, as I mentioned in the comments, weight shouldn't have been an issue because the plane you were in (a 777-300ER), has more than enough engine power to maintain a higher altitude, even fully weighted.

It's actually worth looking at the reverse flight times for routes like this.  Most trans-(North) Atlantic routes are on average about an hour shorter going East->West versus West->East for exactly this reason.  East->West uses as much wind as practical to gain efficiency but West->East this turns into a penalty and flights try to avoid as much wind as possible.  There's a reason European explorers landed in the carribbean on the first go around all those years ago, then had to tack north to catch the westerlies home.

Relevant for visualization : Global Wind Map

There are generally 3 reasons to pick lower altitudes:

At departure your weight would be too much to climb to the desired altitude. Some aircraft are restricted by weight to get up to higher altitudes, usually a thrust-weight issue.
Something's broken on the aircraft requiring it to fly at a lower altitude for safety reasons. As an example, the Air conditioning packs, that control the pressurization on an aircraft, if one is out, the flight might be restricted to a lower altitude so the system can handle the reduced output of the remaining packs to maintain a suitable pressure onboard.
The most likely reason though in this case is to be at an altidude where the headwinds are less than what they are higher. Oftentimes the highest winds in the jetstream start in the FL300+ range, and run generally West-East. So trying to pick an optimal altitude is a factor of getting high enough for efficiency, but not to where you'll be losing that efficiency due to the higher winds aloft.

Why would the plane even be flying with a busted a/c pack though? On all the flights I've been on, pretty much any mechanical issue has led to the problem either being addressed in the ground or a new plane being used. I've almost never been on a flight that was allowed to take off with a mechanical issue.

@Timpanus  It's not that simple.  I would be surprised if any flight you have been on did not have a mechanical issue.

I doubt #1 is true in this case, the 777 practically has enough power to tow another 777 up to cruise altitude, and #2 makes little sense since the flight later climbed higher. #3 is very plausible, though

@JonStory That would be an awesome experiment to see.

haha, I did say "practically" - my point was really that I don't believe a 777 even at MTOW will struggle to climb pretty much straight to FL310/330 (notwithstanding a few steps in the climb to increase airspeed)

They could also have over filled the tank. I'm on an AA flight right now that's choosing to fly lower to burn more fuel.

Unless they're at risk of landing overweight, I can't imagine that they'd be burning money, er... fuel just because the ground crew put in too much. Unless, of course, you've had an announcement telling you so.

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.


text:
How can I triangulate a position using two DMEs?
What is the formula for determining an aircraft's position (latitude, longitude) using barometric altitude and the ranges to two DMEs?

I believe the easiest formula is to take out a map and a pair of compasses (the kind with one pointy end and one pencil end) and draw the arcs.

What you are looking for is the intersection of two spheres (defined by the locations of the DME's and their ranges) and a isobaric surface. This will give you either 2, 1 or 0 solutions. It can be simplified to the intersection of 2 circles and solved mathematically. Typically you'll find two solutions and you need other information to identify which of the two solutions is the aircraft's positions.

We can find the exact method to use online, after all this is a common 3D trigonometry problem. I'll use Michael Geyer
US DoT report: Earth-Referenced Aircraft Navigation and Surveillance Analysis. The principle is:

The two DME distances determine two spheres which intersection is a circle. The aircraft is on this circle.

The aircraft altitude determines a surface (depending on how altitude is measured, it can be a quasi-plane or a surface of constant pressure) which intersects the circle at two points. The coordinates of the points can be computed from the two DME distances and the altitude.

As a matter of fact DME signals at the two points are identical, therefore one must be eliminated by some method.

Note: Historically triangulation was based on measured angles values, methods strictly based on measured ranges (or pseudoranges, that is ranges with an unknown but constant error, like for GNSS) are often termed lateration, e.g. trilateration when using three points.
Intersect two spheres to get a circle
The slant distance determined with DME tells us the aircraft is on the surface of a sphere centered at the DME station, with radius equal to the slant distance. By interrogating two DMEs, two intersecting spheres are determined. The intersection is a circle (pink circle in the figure below). The closer the aircraft is to the line joining the two DME stations (the baseline), the smaller the circle, down to a single point when the aircraft is exactly on the baseline.

Intersect the circle with a surface to get two points
The aircraft is flying in a quasi horizontal plane. This plane intersects the circle at two locations (green points in the figure above) which are symmetrical to the baseline and where the aircraft must be located. By using the direct information we have (altitude and slant ranges), we can compute the coordinates of the two points.
Eliminate the ghost location
At a given time, the aircraft could be located at either points and still receives the same DME signals. In the mathematical solution, this will appear when using a function like $\arcsin(x)$, which gives two angles for the same x value, e.g. 40° (90°-50°) and 140° (90°+50°).
There are several methods to eliminate the virtual position:

Monitor the progress of the aircraft: If the aircraft flies north, the top point moves north while the bottom point moves south. We can detect such illogical trajectory (e.g. using a predictive Kalman filter).

Use a third DME: The third range sphere will intersect the other two at only one point.

Determine aircraft bearing using a VOR, preferably collocated with one of the DME.

In large aircraft, position is determined using multiple means including inertial and GNSS, so it's not difficult to know where the aircraft is approximately.
Determination of the points coordinates
The DME/DME/Elevation case boils down to:

Two DME stations $\small U$ and $\small S$ with known latitudes, longitudes and altitudes ($\small L_U$, $\small \lambda_U$, $\small h_U$ and $\small L_S$, $\small \lambda_S$, $\small h_S$).
An aircraft A with known altitude ($\small h_A$).
Two measured slant distances ($\small d_{UA}$ and $\small d_{SA}$)

$\small C$ is earth center (earth radius is $\small R_e$. Following the method mentioned previously, we execute these steps:

Step 0: Convert slant-ranges to angular distance
Step 1: Solve the spherical triangle for each station
Step 2: Confirm inputs are consistent and a solution exists
Step 3: Solve the spherical triangle USA
Step 4: Compute aircraft latitude and longitude

Step 0: Convert slant-ranges to angular distance
With altitudes and slant ranges known, it is possible to calculate angles $\small \theta_{SA}$ ($\small \widehat{SCA}$) and $\theta_{UA}$ ($\small \widehat{UCA}$) between DME and aircraft. For each DME $\small x$ ($\small x$ being either $\small U$ or $\small S$):
$$\theta_{xA} = 2\space \arcsin \left( \frac{1}{2} \sqrt{\frac{(d_{xA}-h_A+h_x)(d_{xA}+h_A-h_x)}{(R_e+h_x)(R_e+h_A)}} \right)$$
By convention we need to name $\small U$ the station which is westward. This allows us to refer at the aircraft position like "the one south of the baseline".
Step 1: Solve the spherical triangle for each station
The first actual step is to get the angle $\small \theta_{US}$ formed by the two DME stations and earth center:
$$\sin \left( \frac{1}{2}\theta_{US} \right) = \sqrt {\sin^2 \left( \frac{1}{2}(L_S-L_U) \right) + \cos(L_S) \cos(L_U) \sin^2 \left( \frac{1}{2}(\lambda_S-\lambda_U) \right)}$$
where $\small L_U$ and $\small L_S$ are latitudes of $\small U$ and $\small S$ and $\small \lambda_U$ and $\small \lambda_S$ are longitudes of $\small U$ and $\small S$.
We will need to know one of the azimuth at the extremities of the baseline between $\small U$ and $\small S$:
$$ \tan(\psi_{S/U}) = \frac {\cos(L_S) \sin(\lambda_S - \lambda_U)} {\sin(L_S) \cos(L_U) - \cos(L_S) \sin(L_U) \cos(\lambda_S - \lambda_U)} $$
Step 2: Confirm inputs are consistent and a solution exists
If the slant ranges are 10 NM and 15 NM, and the known distance between stations is 30 NM, then there is no actual solution, something must be wrong. This step checks whether the two DME range spheres intersect. We have already computed angles $\small \theta_{UA}$ and $\small \theta_{SA}$ and the one between stations $\small \theta_{US}$:

If $\small \theta_{UA} + \theta_{SA} < \theta_{US}$, then the spheres don't intersect (centers too remote)
If $\small \left| \theta_{UA} - \theta_{SA} \right| > \theta_{US}$, then spheres are concentric, they don't intersect.

Step 3: Solve the spherical triangle USA
Now we know the three sides of the triangle $\small \widehat{USA}$, we can determine any of its angles. We need only the angle with its apex at one station:
$$\cos(\beta_U) = \frac {\cos(\theta_{SA}) - \cos(\theta_{US}) cos(\theta_{UA})} {\sin(\theta_{US}) \sin(\theta_{UA})}$$
Step 4: With all data now available, compute aircraft latitude and longitude
It's time to decide which of the two aircraft positions we want by selecting the corresponding azimuth angle at station $\small U$ (it could be at $\small S$, but we did the previous step for $\small U$):

If $\small A$ is south of $\small US$ baseline (assuming $\small U$ is west of $\small S$): $\small \psi_{A/U} = \psi_{S/U} + \beta_U$

If $\small A$ is north of $\small US$ baseline: $\small \psi_{A/U} = \psi_{S/U} - \beta_U$

Aircraft latitude $\small L_A$:
$$\sin(L_A) = \sin(L_U) \cos(\theta_{UA}) + \cos(L_U) \sin(\theta_{UA}) \cos(\psi_{A/U})$$
Aircraft longitude $\small \lambda_A$:
$$\tan(\lambda_A - \lambda_U) = \frac {\sin(\psi_{A/U}) \sin(\theta_{UA})} {\cos(L_U) \cos(\theta_{UA}) - \sin(L_U) \sin(\theta_{UA}) \cos(\psi_{A/U})}$$

I posted a Python implementation on Stack Overflow.

i really appreciate and respect your effort. This is very informative and unique.

Incredible work @mins


text:
How close can planes fly to each other over the ocean?
While on a recent Air Transat flight from Toronto Pearson to London Gatwick, several hours into the flight and over the Atlantic Ocean, my daughter and I noticed a plane behind ours to the left, flying quite close. Assuming there must be protocol for how close planes can fly to each other, I was more interested than concerned.
It then became apparent that the other plane was flying faster than our plane and coming closer. The plane came close enough for my daughter and me to see all the windows as its path led it to cross in front of our plane. It was only very slightly higher than our plane by mere meters. As it very quickly approached us we lost sight of it as it crossed in front of our path.
My daughter and I figured a crash was imminent. Our plane then altered its path, moving slightly down and to the right.
This was an overnight flight and at the time the cabin lights were turned down and the passengers sleeping. There was no flight crew to speak with at the time and we didn't want to disturb anyone considering we were... well.. still alive.
Upon return from our trip I called Air Transat and spoke with Customer Relations who had the flight records pulled. There was no report of the incident. I cannot believe any regulation could possibly allow for two planes to fly so close to one another under any circumstances. I need to understand what happened here, the distance planes must remain from one another and why such an occurrence would not be logged.
The plane was not marked. It was not a Lear jet but a small, dark, unmarked passenger plane. Thank you for your help. Obviously I am still very disturbed by this event.

Closely related, although specifically about FAA regulations

How recently was this? It would help to have an exact date and flight number.

Did you feel any turbulence after the other plane moved away?

If you provide a date/flight number often we can locate the specific aircraft you saw and see exactly how close it was.

@TomMcW Subtracting two inexact numbers can give much more inexact results. Ate least for the lateral distance. Many aircraft still use INS.

Concerning the possible danger of flying near to each other, consider how near fighter jets come to your aircraft then they intercept it. You could basically talk to them in sign language. Everything else is safety distance to give people time to react, and given you have a lot of space over the ocean, the safety distances are chosen to be rather large, because why not?

@VladimirF Yeah, It would depend on the equipment on the planes and whether or not they were in range of a radar or ads-b receiver. That was the case in the LMI2933 crash. The publicly available data was off due to ins drift. I'm not exactly sure why one would install ads-b out tied to ins, but I guess it saves a few pennies. The Air Transat planes I looked at all appeared to be GPS.

we didn't want to disturb anyone considering we were... well.. still alive.  so, would you have considered disturbing anyone if you weren't still alive? ;-)

A few examples of what 1000 ft separation looks like: 1 2 3 4 5

If two planes which are on a collision course maintain a constant speed, heading, and bearing, each will remain almost stationary in the visual field of the other.  The fact that a plane is visually moving within one's visual field would thus imply that either the planes are not maintaining constant velocity, or they are not on a collision course.

My daughter and I figured a crash was imminent It wasn't.  Unless you are in a situation of constant bearing / decreasing range, you aren't going to crash.  Suggest you go to Google and research the term "relative motion."

@Michael: If I ever get the chance to haunt someone, I'm all over it.

"My daughter and I figured a crash was imminent" - why didn't you pull the emergency brake then?

Please note that humans perceive shorter length than reality, when there are nothing for reference in between the observed object an the observer.

I'd be very interested to know whether @Wendy found the answers to this question reassuring. Please ignore some of the superior and condescending comments that have been made - some people think that knowing something that someone else doesn't entitles them to forget their manners. In fact I see that Wendy is no longer registered.I'm not surprised, given the tone of some of the comments above.

It was only very slightly higher than our plane by mere meters.

You think you saw a plane at the exact same vertical level as yours, when in fact it was at least 300 metres (1000 feet) above or below your level. It can be very hard to judge differences in level for the untrained eye, especially over the ocean and at night when there is nothing to reference for scale. Your confusion is understandable, but there was absolutely no safety risk here.
The minimum vertical separation between two aircraft is 1000 feet, and the plane you saw was - with 100% certainty - at least 1000 feet above or below you. This is ensured by air traffic control and a ton of complex regulations and rules governing air traffic.
When over the ocean, where no radar coverage exists, if two planes are flying at the same level, they will either be at least 10 minutes flying time apart (if following the same route), or 25 nautical miles (about 50 kilometres) if flying on parallel routes. Over land where there is radar, two aircraft at the same level will generally be at least 5 nautical miles apart (10 kilometres). But when 1000 feet or more vertical separation exist, aircraft can cross each others paths without any risk. It is perfectly normal for aircraft to fly this close, but passengers seem to take notice more often over the ocean, probably because there is nothing else to look at.
There was no risk of collision during your flight. If, for some inexplicable reason, the standard separation described above was violated, pilots and air traffic controllers would have responded immediately to establish separation again, long before any sort of collision risk would occur. There is very reliable technology in place to warn pilots and air traffic controllers if aircraft are getting too close, and they are trained to react to such warnings without delay.
For more information on separation, please see my answer on "How are aircraft separated at high altitudes?"

If you don't think it's difficult to estimate distances, go outside during daylight and try to estimate how tall the nearest radio or (cell) phone tower or windmill is. Then using the references in the answers here go look up how tall it actually is. For the untrained eye, estimating height/distance is quite difficult.

Since the OP is 'still very disturbed by this event' is it worth mentioning TCAS in the penultimate paragraph?  https://en.wikipedia.org/wiki/Traffic_collision_avoidance_system

@DaveGremlin Since OP clearly knows quite little about aviation, I wanted to keep the answer simplistic. I added a general note about technology instead.

@DaveGremlin good point about TCAS. If a collision was likely the TCAS on both aircraft would divert the planes away from each other without pilot input.

@mickburkejnr No it wouldn't. TCAS provides a warning to the pilots, it does not control the plane. It's up to the pilots to follow the recommended action of TCAS

@J.Hougaard On the Airbus planes TCAS is linked to the flight director, so if the autopilot is engaged it will automatically respond to the TCAS direction. If autopilot isn't engaged then it's just an advisory to the pilot for the pilot to make the input. I should've made that clearer, I apologise.

Never heard of that, thanks. https://www.skybrary.aero/index.php/Autopilot/Flight_Director_(AP/FD)_TCAS_capability

Also seems like it'd be harder to judge distances when you have no other frames of reference like when you're over the Ocean.

And even 10 km of separation at jet airliner speeds is a good minute or so of flying. Even if the two are approaching each other head on, there's still half a minute to escape from the situation.

Short of having a PPL, I'm not involved in aviation and so take this with a grain of salt. It seems strange to me that you say this "with 100% certainty". Have planes not crashed because separation was not maintained?

@canadianer I guess I'm 99,99% sure and decided to round up to 100 ;)

@mickburkejnr per the Our plane then altered its path, moving slightly down and to the right. part maybe?

@Michael Shouldn't a TCAS activiation be grounds for a flight report and a very hard slap on some wrists?

To give a sense of scale to the height separation the Eiffel tower is just around 1k ft. tip of Empire state building is 1.4 k ft.

Are there air traffic controllers over the open ocean?

@PaüloEbermann Yes.

This is an excellent question, and helps illuminate several important aspects of the way perception works in aviation. But first...
Any near-miss or other air-proximity incident would have been reported
If there had been any risk of a collision, it would have been reported, unless somehow (and this is astoundingly unlikely) the entire flight crew of both aircraft were entirely piratical.
But flight crews are not swashbuckling daredevils; they do everything by the book, because that's what keeps them alive to fly another day, and because everything in their training and professional discipline is about following procedures correctly.
Even if there were not a risk of collision, but the merest compromising of safety, the incident would have been reported.
What you saw
But let's consider what you saw. Our binocular vision is excellent; it can track movements, and judge speeds, sizes, angles and relative position with amazing accuracy and precise judgements, which is why we human beings can do things like return Roger Federer's serve and shoot apples off people's heads with arrows.
However, our binocular vision can do all these wonderful things only when it's operating in a rich and reliable frame of reference. In an aircraft, at night, over the ocean, we lose almost all of the reference that allows us to make accurate and precise judgements. You could be looking at a small aircraft a short distance away or a huge one far away, and you'll have little chance of knowing which. It gets even harder to judge speeds. Relative position can also be very hard to judge.
However compelling the feeling that you know what you saw, it's simply not reliable.
In this case, the compelling evidence of your perception led you to conclude that there was a risk. In aviation, we usually hear about the opposite case: where trust in compelling-but-unreliable perception causes a pilot to underestimate or even just ignore a risk. Pilots learn that perception is not a reliable friend, and that senses that work very well when playing tennis or with crossbows are hopelessly inadequate in the air.
Instead, they place their trust in a battery of proven instruments, from simple things like gyroscopes and compasses that have been key to flight safety for a century or more, to advanced radar systems, and industry wide systems and processes. They are what keeps flight safe.
It's hard to ignore the clamouring of one's alarmed perceptions, but the fact is that when you climb on board on airliner you should accept that nothing you will see or feel for the next few hours is a good indication of what it really is.
What if the pilot took evasive action?
You mention that your flight changed course slightly, with the implication that this may have been evasive action.
If your pilot had been required to take some sort of emergency last-second evasive action to avoid a collision, not one of your sleeping fellow passengers would have remained asleep: those of you not strapped down would have been hurled to the ceiling or slammed to the floor and your stomach would be heaving in a different direction from the rest of you.
You'd really know about it, in other words. And then there would be plenty of aviation industry paperwork to follow.
However, that would be an extraordinarily rare thing. Evasive action, in the still very rare cases when it is required, is taken well before it's necessary to hurl the plane around in the sky to avoid something at close quarters.
Aircraft of the kind you're talking about are fitted with equipment that monitors their sector of the sky (for miles and miles around) for other aircraft, and will advise each flight crew to climb or descend appropriately so that there is not a proximity risk.
Either way, it certainly doesn't sound like you experienced evasive action at that moment.
On being disturbed
It's completely natural to be disturbed by what you saw - but if you accept that aviation is completely unnatural as far as our senses and perception go, and they just don't work very well at making good judgements in that context, that might help.
Even if you can't let go of the reports of your perceptions (I can't), knowing that the reality is otherwise can still help.
In short: anyone else looking out of the window may well have been alarmed by what they saw. Once that moment of alarm has passed though, what you know can help prevent it from continuing to disturb.

Very good! "It's hard to ignore the clamouring of one's alarmed perceptions". Perception (auditive, visual...) is pre-processed by filters in the brain. Those filters deliver a modified information to other parts of the brain which need it. Those filters are built during our childhood from experience. This is why we'll keep affirming squares A and B are not of the same color in this checkerboard, while actually they are. Here, our brain trusts the filters (A is black, B is white), and cannot retrieve the original colors.

Good answer, except the bit about evasive action. In situation like this, evasive action would be taken based on TCAS advisory and those leave enough time so there is no need for drastic manoeuvres. Few notice response to TCAS RA when it happens. However, there is a way to tell this was not an evasive manoeuvre: evasive manoeuvres are always vertical. Both because TCAS has accurate method for comparing altitudes, but not for solving how the horizontal paths intersect, and because climb or descent are initiated faster than a turn.

@JanHudec Edited to clarify that I was describing a hypothetical WTF is that? emergency manoeuvre, not TCAS-initiated evasive action.

@JanHudec Being that OP was able to observe the incoming plane before the course correction, I think we can assume the maneuver didn't occur (because it wasn't necessary)

@corsiKa, well, I would believe the OP that some manoeuvre did occur—it just was a completely coincidental course correction (the North Atlantic tracks are not straight) and not evasive manoeuvre.

Still couldn't have done any harm to report to the pilots when they thought they were on a 'collision course'

I know this sort of comment is frowned upon, but I think this is among the best answers ever written on this entire site! I liked specifically that you discuss aviation from the POV of both the experienced pilot and the inexperienced passenger - while the latter believes in their "compelling-but-unreliable perception", the former knows to trust the instruments and ATC, even at the expense of disregarding what they see out the window - especially above FL100

A "small" transatlantic plane probably isn't very small -- it was probably further away than you think.  Compare these silhouettes (can't embed due to image rights, also can't vouch for accuracy):

737 (31m)
757 (47m)
767 (49--61m)
777 (64--74m)

(Just look at the first and last for a quick indication of what I mean)
In brackets are the lengths (ranges where I don't know which model the silhouette represents).  A trained eye could identify the model, then make a decent estimate of the distance.  A untrained eye, with no distance cues, would really struggle to rank them in order of size, despite the factor of around 2 difference in length betwen a 737-500 and the widebodies.  So if you're used to seeing 737s fairly close at your regional airport and then see a 777 fly past, it will seem half as far away as you think based on size alone -- and in an empty sky things seem closer than they are.

Right, shapes are very similar, even a Messerschmitt 262 doesn't look that different than an A350.  So a distant 747 will look like a near Learjet.   On Bush's famous Thankgsiving 2003 trip to Baghdad, another pilot radioed that he thought he saw Air Force One, they radioed back saying "we're just a Learjet", and the pilots bought it.   So it really is hard to tell.

@Harper an extreme example but a good one.  About 20 years ago I had a little experience with silhouettes of aircraft on approach (almost head-on) but never got to be a real expert.  Even then I had the advantages of familiar conditions and ground cues

Something to note here would be that modern aircraft contain a Traffic collision avoidance system (TCAS). So pilots in both aircraft would have been notified that they were on a collision and one would be told to change altitude. The system is so reliable that in the event TCAS and ATC orders conflict, TCAS is to be obeyed (due to a midair collision over Germany in 2002)

When an [Resolution advisory (RA)] is issued, pilots are expected to respond immediately to the RA unless doing so would jeopardize the safe operation of the flight. This means that aircraft will at times have to manoeuver contrary to ATC instructions or disregard ATC instructions. In these cases, the controller is no longer responsible for separation of the aircraft involved in the RA until the conflict is terminated.

So at the bare minimum, your aircraft were separated by enough distance not to set off the alarm (600 ft)

Aircraft operating within the NAT High Level Airspace(Atlantic Ocean), from Flight level 285 and 420 inclusive are required to conform to the Reduced Vertical Separation Minimum (RVSM) equipment requirements.
This means that they are required to have an autopilot capable of maintaining 1000ft vertical separation and have equipment to alert them if the aircraft strays from the assigned level. In addition in order to operate in RVSM airspace you must have a Traffic Collision and Avoidance System (TCAS) fitted.
So in the situation you describe the autopilot would have been on maintaining the cleared level and the TCAS would of been showing the aircraft that passed you on the display in the flight deck. If the other aircraft strayed from its cleared level (1000ft clear) then the TCAS would of alerted the crew and if required provide a resolution advisory to climb or descend. This would be the case in both aircraft involved.

authors: Vladimir F Героям слава


text:
What happens if an aircraft's hydraulic system starts leaking during a flight?
What will happen if hydraulic fluid starts leaking during a flight? What will happen to the overall performance of the flight, and how will the pilot compensate for the loss of the system?

It's more or less like leaking blood. If the leak is slow then you are OK until you really run out of fluid, which could take a while. If the leak is so wide that you can feel the loss of pressure, then you will be in trouble in a few seconds.

it also depends on whether or not the plane's hydraulic system has a redundant backup system which comes into play upon failure of the primary system. then the issue becomes whether or not the failure has affected both systems or only the primary.

The pilots hear a ding, and an annunciator lights up. One pilot finishes the flight while another flips through a 900 page book, looking for a procedure, when they get to the gate they give up on the 900 page book and call maintenance. The passenger is 2B complains about the cabin being too cold. Someone in 41C never got their rum and coke. The next flight is delayed by 47 minutes.

To quote an unnamed aircraft maintainer in response to a question about an apparent hydraulic leak, "If it ain't leaking, it's empty. We'll mop it up and top it off. You're good to go."

That depends on the aeroplane. On the B737 for instance, there are three independent hydraulic systems: System A, System B, and Standby System. Normally Systems A and B are operating and Standy is off, only switched ON when necessary from a malfunction.
The flight systems are powered redundantly, with more than one hydraulic system powering the essential aircraft systems. The following systems are powered by the hydraulics:

The hydraulic systems are each redundantly powered as well. For instance hydraulic system A is powered by an engine driven pump and an electrical AC pump. System A is protected from leaks in the engine driven pump lines by a stand-pipe: should a leak occur there, fluid leaks away until the fluid level reaches the stand-pipe, at which point the fluid level is approx. 20% and the engine driven pump circuitry is empty. System pressure is then maintained by the electric pump. Should a leak develop in the electric pump circuitry, the fluid quantity in system A reser- voir, and therefore system pressure, steadily drop to zero.

System B has similar anti-leak features, with a stand-pipe that allows for the Power Transfer Unit (PTU) to operate on the remaining fluid. The PTU is a dual hydraulic pump/motor: one end is driven by System A, the other end can pressurise the fluid in System B.

Do we need gear up landing if the system A fails? Looks strange.

@h22 agreed - that looks funny. Gear will probably lower in a hydraulic failure by gravity & wind pressure, though.


text:
Why is the F-16's service ceiling 50,000ft?
What defines the service ceiling for aircraft, in particular the F-16?
I suppose, as with almost everything, this depends on the aircraft, the engine type, etc. While I'm fine with a comprehensive answer including some discussions for different types of aircraft, I'm just limiting this to the F-16 to make it specific enough.
Basically, what exactly is it that prevents the F-16 from exceeding 50,000 ft?
Imagine an F-16 at 50,000 ft in a clean configuration, full afterburner, having reached around mach 2, then the aircraft attempts to climb at maximum rate of climb.
What will happen?
Is the engine unable to ingest enough air? Making the air fuel mixture too lean, eventually resulting in flameout or damage to the engine?
Is it due to the aircraft being unable to produce enough lift at this altitude? How much lift does an F-16 need anyway? Within a certain envelope, the thrust to weight ratio of the F-16 supposedly exceeds 1 and the aircraft can climb vertically -- however, I don't imagine this to hold true for very high altitudes, probably only within an narrow optimal set of parameters?
Is it a combination of the two? Which hits the F-16 first?

Related

Also related

Very related, indeed. I'm still very curious what exactly would happen in the case of the F-16 though.